Python Programming Reading And Writing Files Complete Guide

Python Programming: Reading and Writing Files

File Modes in Python

When you work with files in Python, the first step is understanding the different file modes. These modes dictate how the file is accessed and modified once it's opened. Here are some of the most common file modes:

1. 'r' - Read (default mode). Opens a file for reading, error if the file does not exist.
2. 'w' - Write. Opens a file for writing, creates the file if it does not exist; overwrites the file if it exists.
3. 'x' - Create. Creates a new file, returns an error if the file already exists.
4. 'a' - Append. Opens a file for appending, creates the file if it does not exist.
5. 'b' - Binary. Used alongside other modes for binary files.
6. 't' - Text (default mode). Used alongside other modes for text files.
7. '+' - Update. Used alongside other modes (e.g., 'r+') to allow both reading and writing.

For instance, 'rb' mode is used to read a file in binary format, and 'wt' is used to write a file in text mode.

Opening a File

To open a file in Python, use the built-in open() function, which requires a minimum of two parameters:

• file (string): The path to the file.
• mode (string): The mode in which the file opens.

Here’s an example of opening a file for writing:

file = open('example.txt', 'w')

Alternatively, it’s a good practice to use the with statement because it automatically manages file closing even if an exception is raised:

with open('example.txt', 'w') as file:
    # perform file operations

Reading from a File

Python provides several methods to read from files. Here are the most commonly used ones:

• read(): Reads the entire content of the file into a string.

  with open('example.txt', 'r') as file:
      content = file.read()
      print(content)
  

• readline(): Reads a single line from the file.

  with open('example.txt', 'r') as file:
      line = file.readline()
      print(line)
  

• readlines(): Reads all lines in the file and returns them as a list where each element is a line.

  with open('example.txt', 'r') as file:
      lines = file.readlines()
      for line in lines:
          print(line)
  

• Using a loop: Iterates through the file object, reading each line one by one.

  with open('example.txt', 'r') as file:
      for line in file:
          print(line)
  

Writing to a File

Python also provides multiple methods to write to files:

• write(string): Writes a string to the file. If the file does not exist, it will be created.

  with open('example.txt', 'w') as file:
      file.write('Hello, world!')
  

• writelines(sequence): Writes a sequence of strings to the file. There won’t be any automatic newline characters, so make sure to include them as required.

  with open('example.txt', 'w') as file:
      lines = ['Hello\n', 'World\n']
      file.writelines(lines)
  

• Appending: To add content to the end of a file rather than overwriting existing content, use the append mode ('a').

  with open('example.txt', 'a') as file:
      file.write('\nGoodbye, world!')
  

Using os and shutil Modules

The os and shutil modules provide functions to interact with file system features.

• os.path.exists(path): Checks whether a file or directory exists at the specified path.

  import os
  if os.path.exists('example.txt'):
      print("File exists")
  

• os.remove(path): Removes a file at the specified path.

  import os
  os.remove('example.txt')
  

• os.rename(src, dst): Renames a file or directory from src to dst.

  import os
  os.rename('old_example.txt', 'new_example.txt')
  

• ** shutil.copy(src, dst)**: Copies a file from src to dst.

  import shutil
  shutil.copy('example.txt', 'copy_of_example.txt')
  

Error Handling

Files operations might fail due to various reasons, like the file does not exist, read/write permissions are restricted, etc. Handling these exceptions gracefully is crucial.

• try-except block: A standard approach to handle exceptions in file operations.

  try:
      with open('example.txt', 'r') as file:
          content = file.read()
  except FileNotFoundError:
      print('File not found')
  except IOError:
      print('Error occurred while handling file')
  

Working with CSV Files

CSV (Comma-Separated Values) files are commonly used data formats. Python supports working directly with CSV files using the csv module. Here’s how you can read from and write to a CSV file:

• csv.reader(fileobj): Reads from a CSV file.

  import csv
  with open('example.csv', mode='r') as file:
      reader = csv.reader(file)
      for row in reader:
          print(row)
  

• csv.writer(fileobj): Writes to a CSV file.

  import csv
  with open('example.csv', mode='w', newline='') as file:
      writer = csv.writer(file)
      writer.writerow(['Name', 'Age'])
      writer.writerow(['John Doe', '28'])
  

JSON File Handling

JSON (JavaScript Object Notation) files are excellent for exchanging data. Python provides the json module for parsing and creating JSON data. Key methods include:

• json.load(fileobj): Reads JSON data from a file and converts it into a Python dictionary.

  import json
  with open('data.json', 'r') as file:
      data = json.load(file)
      print(data)
  

• json.dump(obj, fileobj): Converts a Python dictionary into JSON data and writes it to a file.

  import json
  data = {'name': 'John Doe', 'age': 28}
  with open('data.json', 'w') as file:
      json.dump(data, file, indent=4)
  

Binary File Operations

Working with binary files is similar, but you should use 'b' mode when opening the file.

Reading binary data:

with open('photo.jpg', 'rb') as file:
    photo_data = file.read()

Writing binary data: